I added a K type thermocouple(actually took a couple of goes as the ifrst one melted!)I took it apart, cut off the smouldering ends, joined the new ends togetherused heat resistant (fibre glass?) insulation this time

disconnected all the oven control gear and wired it via a triactriac controlled by 'duino of course

software attempts to match the profile for reflow ovens

anyway - time for some pictures

here's the triac driver boardit's inside the oven to keep mains voltage well away from small children and idiots(er and me )

2nd picture shows the much reduced internal wiring

3rd picture shows the first board "wot I made"it's a micro 'duino

once Nick Gammon helped me with the bootloader - it worked!

4th picture is part of a range of camera kit we're sellingall the SMD parts sorted in < 10 minutes!

the two wires are insulated with what looks like glass insulationthen slipped inside a stainless steel "knitted" (thank you Mrs Noah) outer jacket

trouble is at the business end the trimming was awfulwith strands of wire touching the probeand shorting it out intermittently

so - trimmed it back - much easier said than done stainless steel is tough!wrapped the end of the metal in heat shrink - just to hold it while I re-assembled

temperature readings now rock steady

but

as the probe is inside a metal sleeve, there does seem to be some inertia in the measurement nowthe graph below shows the problem- (apparent) delay in getting started- overshoot at the intermediate temperature points

a naked thermocouple is much more responsive(see the original curve posted earlier)

I may well add PID processing - which should stop the overshootnext decision after that's all working

oh and for amusement here's a picture of the first probenot completely heat proof methinks!

as the probe is inside a metal sleeve, there does seem to be some inertia in the measurement now

"Dead-time" in PID jargon.

Quote

I may well add PID processing - which should stop the overshoot

Not necessarily. There is a conflict between getting the response you want, the dead-time, and overshoot. If possible, you should first strive to reduce the dead-time as much as possible. That will make working with PID much much easier.